The supply of proper levels of bioavailable essential minerals in daily diets is important for maintaining human health. It is well known that, for example, calcium deficiencies may induce osteoporosis, immunological diseases, hypertension, arthritis, colon cancer, diabetes, and obesity, while zinc deficiencies may result in prolonged healing of wounds, retarded growth, delayed sexual maturity, post-pregnancy stretch marks, fatigue, and susceptibility to infection.
It is also well known that metals chelated by amino acids are important sources of trace minerals essential for human, animal, and plant nutrition. The health advantages of supplementing nutritional inputs with amino acid chelates for human and animal consumption are well documented in the prior art. Active transport mechanisms for uptake of amino acids by mucosal cells also sequester metals chelated to amino acids an active transport as solely amino acids, whereas such metals supplied in an inorganic form or as organic salts are not readily digestable.
Amino acid chelates refer to the products formed by the reaction of naturally occurring amino acids with metal ions to produce one or more five-member rings with structures that are defined by the metal atom, the carboxyl oxygen, the carbonyl carbon, the α-carbon and the α-amino acid nitrogen moities. However, the actual structure architecture of each amino acid chelate is determined by the coordination number of the central metal ion and the molar ratio of ligand (i.e., amino acid) to metal. The coordination number of a specified atom in a chemical species is the number of other atoms that can be directly linked to that atom in a particular reaction. For example, it is known that the zinc, magnesium and cobalt each have a coordination number of 6, while calcium may have a coordination number of 6 or 8. However, Pidcock and Moore (2001, J. Biol. Inorg. Chem. 6, 479-489) have reported that the average coordination number for Ca2+ was 6, based on surveys of X-ray structures of numerous Ca2+-containing proteins.
Amino acid chelates are generally produced by first dissolving a water-soluble metal salt in water, and then adding in the amino acid ligand to provide a metal to ligand molar ratio of about 1:1 to 1:4. The water-soluble metal salts used as starting materials for methods to chelate amino acids typically provide the metal complexed to an anion, most commonly sulfate ions or chloride ions. Although some prior art methods provide steps for removal of excess anions during the production of amino acid chelates, significant amounts of anions typically remain trapped within the chelate ring-structures and/or directly bound to the metal cations sequestered within the amino acid rings. Numerous disadvantages are associated with amino acid chelates produced from metal salts wherein anions are bound to the metal cations. For example, ingestion of chelated amino acids for extended periods of time may result in the accumulation of sulfate and/or chloride anions in body tissues to the extent where these anions can negatively affect general health and well being. Amino acid chelates containing significant amounts of anions often exhibit poor solubility and stability properties, particularly in strong acid or alkaline environments, or in the presence of other ions such as phosphates. Furthermore, the presence of anions, such as sulfate or chloride ions, in amino acid chelates can often result in undesirable or objectionable tastes and odors when such amino acid chelates are incorporated into foodstuffs and beverages.
Various approaches have been disclosed in the prior art for ameliorating the disadvantages of amino acid chelates containing anions as a consequence of the methods by which they were produced. For example, U.S. Pat. Nos. 5,504,055 and 6,299,914 teach that the solubility and stability of such amino acid chelates can be improved by adding in pH adjustors and suspension stabilizers during the chelation process. U.S. Pat. No. 6,458,981 discloses a method for reducing the anionic content of amino acid chelate products by supplying along with the desired metal in the form of a metal sulfate salt, a hydroxide or calcium hydroxide for reacting with and precipitating free sulfate ions from the reaction mixture after which, the precipitated calcium sulfate is separated from the amino acid chelate product.